1. Technical Field
The invention relates to an optical module. Particularly, the invention relates to a light source module adapted to a display apparatus.
2. Related Art
Light source modules applied to display apparatuses are mainly divided into direct type light source modules and side type light source modules. Regarding the direct type light source module, light emitting elements can be used in collaboration with a secondary optical lens to provide a uniform planar light source. The secondary optical lens is used for reducing the number of used light emitting elements (for example, the number of used light emitting diodes) and for decreasing a whole thickness of the light source module, which is more in line with demands of energy-saving and carbon reduction, lightweight and thin thickness on products in the market. However, since the cost of the secondary optical lens is relatively high, the direct type light source module has the disadvantage of high cost. On the other hand, there is another type of the direct type light source module without using the secondary optical lens, and compared to the design that the light emitting elements are used in collaboration with the secondary optical lens, the secondary optical lens is saved, and the structure of such light source module is relatively simple and the cost thereof is lower. However, the number of the used light emitting elements of such direct type light source module is greater, which is liable to decrease system reliability, and since a certain light mixing distance has to be maintained, the whole thickness of the light source module is hard to be decreased.
As shown in FIG. 1A and FIG. 1B, recently, a direct type light source mode mainly composed of a light emitting element 10, a reflective lamp cover 20, a diffusion plate 30, and a bottom reflector 40 is developed, in which the reflective lamp cover 20 reflects a light beam emitted by the light emitting element 10 to the bottom reflector 40, and the bottom reflector 40 reflects the light beam to the diffusion plate 30 to emit light. According to such structure design, since the secondary optical lens and the light guide plate are omitted, the light source module has lower cost and thinner thickness, and has higher competitiveness. However, the existing reflective lamp cover has an uneven light emitting effect, and a main reason thereof is that a part of the light beam emitted by the light emitting element 10 may directly enter the diffusion plate 30 to emit out. Since such part of the light beam directly emits out without being functioned (for example, diffused) by the bottom reflector 40, a light intensity thereof is concentrated, which is liable to produce a bright band at a corresponding region 30a of the diffusion plate 30. Particularly, under a structure of a large-size light source module, the light beam that directly enters the diffusion plate 30 for emitting out is liable to emit out at the region 30a adjacent to the light emitting element 10, such that the bright band phenomenon of the diffusion plate 30 at the region 30a adjacent to the light emitting element 10 becomes more obvious. As shown in FIG. 1B, under the structure of the large-size light source module, the position of the region 30a of the diffusion plate 30 where the bright band is produced is approximately spaced by a distance D from one end of the diffusion plate 30 adjacent to the light emitting element 10, and the distance D is about ⅛ to ⅜ of a width T of the diffusion plate 30.
According to the existing technique, the bright band phenomenon is mitigated by extending a width of an upper half of the reflective lamp cover or increasing a height of the upper half of the reflective lamp cover. However, extension of the width of the upper half of the reflective lamp cover may decrease light emitting efficiency of the light source module and causes increase of invalid region, and increase of the height of the upper half of the reflective lamp cover may increase a whole thickness of the light source module. Therefore, how to resolve the bright band problem while maintaining the existing advantages (for example, a thin thickness) of the direct type light source module is an important issue to be developed.
Taiwan Patent No. 569067 discloses an arc reflective plate having protruding structures at upper and lower inner surfaces for eliminating or decreasing an edge bright band. Taiwan Patent No. I332596 discloses a reflective lamp cover including micro protruding structures for reducing light leakage at a bonding surface. Taiwan Patent No. M263519 discloses an implementation for extending a width of a lamp cover to prevent generating a bright band. Taiwan Patent No. M444487U1 and Taiwan Patent Publication No. 200907229 and 201205001A1 respectively disclose different reflective lamp covers, and Taiwan Patent No. I390303B1 discloses a bottom reflector of a light source module.